Numerous attempts have been made over a period of more than forty years to develop ice detection systems as illustrated by Hall U.S. Pat. No. 2,269,019; Peters, et al. No. 2,359,737; Thoma No. 4,327,286; Forgue No. 4,333,004; Kovaca No. 4,379,227; Chamuel No. 4,461,178 and Magenheim et al., No. 4,470,123, the disclosures of which are incorporated herein by reference.
In recent years efforts have been made to develop fiber optic technology for various purposes including the use of a bent fiber optic refractometer device for measurement of salinity in double diffusive thermohaline systems as described in Rev. Sci. Instrum. 56(2), Feb. 1985 of the American Institute of Physics, the disclosure of which is incorporated herein by reference. Powell U.S. Pat. No. 4,256,403, the disclosure of which is incorporated herein by reference, discloses a water contaminate and fuel density detector using a longitudinally extending body of light transmitting material with light emitting means at one end to provide a group of divergent rays in angularly disposed light emission paths onto a plurality of vertically spaced light sensors for producing a signal corresponding to the index of refraction indicating the density of the fuel, while also indicating the presence of water in the fuel.
In general, the present invention utilizes a sheathed and/or coated optical fiber means having a first sheathed and/or coated light path portion connected to a light emitting device for transmitting light from the light emitting device along a first covered light transmission path, an intermediate, unsheathed, exposed core portion having an abraded peripheral surface for providing a sensor means, and a second sheathed and/or coated path portion connected to a light receiving device for receiving transmitted light from the light source and generating variable output signals dependent on characteristics of received light. The optical fiber device is constructed and arranged to prevent light loss in the first path portion and the second path portion with variable light losses occurring in the intermediate portion depending upon variations in environmental conditions at the intermediate portion. The variable light losses in the intermediate portion are dependent on the reflection and refraction characteristics of the intermediate portion of the optical fiber device and the reflection and refraction and absorption characteristics of the environmental medium in contact with the intermediate portion. Since various characteristics, such as reflection, refraction, heat of fusion, rate of temperature change in various phases, etc., of various mediums, such as air, water, ice, corn oil, gasoline, etc., are known or can be determined, the amount of light loss in the intermediate portion can be calculated with respect to various surrounding mediums. Differences in the amount of light received by the light measuring device can be used to indicate the nature or phase (i.e., solid, liquid, gaseous) of the environmental medium in contact with an outer surface of the intermediate portion of the optical fiber device.
The present invention provides an apparatus and methods for detecting the buildup of ice on surfaces, which apparatus and methods are capable of distinguishing between water and ice on the surface being observed, and for other purposes such as detecting the presence of water in gasoline or oil or level of liquids in a vessel. The detection of the buildup of ice on surfaces is provided by measurement of the difference between the light energy absorption and refractive indices of dissimilar materials using a sensor probe of special design. The system of the present invention provides for automatic and real time detection of water and icing on surfaces by monitoring variations in light energy transmitted through a bent optical fiber having a specially processed sensitive area at its bend. The sensitive area is preferably positioned adjacent, on, about or within the surface on which icing is to be detected. Because of differences in the optical indices of refraction and energy absorption characteristics of air, water and ice, the presence of one of these mediums on the surface of the optical fiber core at the processed sensitive area, will cause a proportional and characteristic attenuation of the light energy passing through the optical fiber. The resultant observed changes in light energy transmission can be interpreted mathematically to produce an indication of the presence of ice or other material on the surface being tested. A reference optical circuit may be used to provide compensation for variations in input energy levels, temperature, physical stress, ambient light, etc. Light energy of different wave lengths and energy levels may be used to compensate for or avoid interference with measurement that could be produced by differences in ambient lighting conditions or for the detection of other conditions and materials using the principle of characteristic absorption and resonance. The rate of ice accretion or precipitation may also be measured by the use of a capacitance system or an electrically conductive heater wire positioned on or about the sensitized area of the optical fiber.